post_proc: fix crash in offload effect bundle during stop output

Effect bundle stop() frees mixer contol before doing module stop(),
whereas module's stop() still needs this control to send disable
command down the layer.
Crash is observed if memory associated with effect control is reused
and gets altered by the time mixer control is completed.
Move mixer control's deletion after module's stop() to fix this issue.

CRs-Fixed: 860604
Change-Id: Ia8b6d5f847b69392afbda1ba77fc740a47aba25d